The processing of color photosensitive materials comprises basically the color development process and the desilvering process. The exposed color photosensitive material first undergoes the color development process, in which the silver halide is reduced to give silver by the color developing agent and the oxidized color developing agent reacts with the coupler to form a dye image. Then the color photosensitive material undergoes the desilvering process, in which the silver formed in the preceding process is oxidized by the action of an oxidizing agent (commonly called a bleaching agent). Finally the oxidized silver is solbilized and removed from the photosensitive material by a chelating agent for silver ions (commonly called a fixing agent). As a result, a dye image is formed on the color photosensitive material. In the actual development processing, the above-mentioned main processes--color development and desilvering--are accompanied by auxiliary processes to ensure the photographic and physical properties of the image and to preserve the image for a long time. They include, for example, the hardening bath which prevents the sensitive layer from getting excessively soft during processing, the stopping bath which effectively stops the development reaction, the stabilizing bath which stabilizes the image, and the bath to remove the backing layer of the base.
The desilvering process may be accomplished in a single bath which contains a bleaching agent and a fixing agent. It may also be accomplished in two separate baths for bleaching and fixing.
Bleaching agents in general use include red prussiate, potassium bichromate, ferric ion complex salt, and persulfate. A bleaching solution of red prussiate performs outstanding bleaching action; but it has a disadvantage that the ferricyanide ions and ferrocyanide ions, which are reduced forms of the ferricyanide ions, are discharged from the processing equipment and form highly toxic cyanide compounds upon photooxidation. Therefore, there has been a demand for a new bleaching agent that will replace red prussiate.
A ferric ion commplex salt is used as a bleaching agent of the bleach-fix bath for color photographic paper. (See German Pat. Nos. 866,605 and 966,410, and British Pat. Nos. 746,567, 933,088, and 1,014,396.) The bleaching solution or bleach-fix solution containing a ferric ion complex salt is weak in oxidation. Therefore, it takes a long time for the processing of color photosensitive materials which contain silver halides in high concentrations and also contain silver iodobromide.
Since bleaching with red prussiate or a ferric ion complex salt causes water pollution, bleaching with no metallic ions or bleaching with a persulfate is preferable. However, the persulfate bleaching solution is weaker in bleaching power than ferric ion complex salts and takes an extremely long time for bleaching. Thus there has been a demand for a method for accelerating the bleaching with a persulfate which can be applied to high-speed color photosensitive materials containing a large amount of silver halides.
The bleaching with a persulfate is accelerated by adding an amino compound to the treating bath such as the bleaching bath, the bleach-fix bath, or the prebath thereof, according to the conventional methods as disclosed in U.S. Pat. Nos. 3,772,020 and 3,893,858 and "Research Disclosure" No. 15704.
These methods still take a considerably long time for complete bleaching. Moreover, the addition of an amino compound to the bath is not preferable because it usually gives off an offensive odor. In addition, these methods are unable to bleach completely the color photosensitive materials having colloidal silver layers (such as yellow filter layer and antihalation layer) and hence containing a large amount of silver.